Directed self-assembly of two kinds of nanoparticles utilizing monolayer films of diblock copolymer micelles

We demonstrated a self-assembly of two different kinds of nanoparticles simultaneously directed on a monolayer film of diblock copolymer micelles via physical and chemical arrangements. We first incorporated gold nanoparticles physically around the micelles of a monolayer film of PS-PVP micelles having a short-range hexagonal order. Iron oxide nanoparticles were then synthesized chemically in the PVP core area of the ordered micelles, resulting in a mosaic nanopattern of magnetic iron oxide nanoparticles surrounded by metallic gold nanoparticles. Thus, we were able to direct two kinds of nanoparticles to self-assemble in the specific positions as an example of controlled fabrication of nanometer-sized building blocks.     

Catalytic generation of activated carboxylates from enals: a product-determining role for the base

N-Heterocycle carbenes generated in situ from imidazolium or triazolium salts and bases react with enals, leading to the catalytic generation of homoenolates. The fate of these intermediates is determined by the catalytic base: strong bases such as (t)BuOK lead to carbon-carbon bond formation, while weaker bases allow protonation of the homoenolate and subsequent generation of activated carboxylates. This discovery, along with the design of a new triazolium precatalyst, enables the catalytic, atom-economical redox esterification of enals. [reaction: see text]     

Analysis of tofisopam in human serum by column-switching semi-micro high-performance liquid chromatography and evaluation of tofisopam bioequivalency

A rapid and sensitive column-switching semi-micro HPLC method is described for the direct analysis of tofisopam in human serum. The sample (100 microL) was directly injected onto the precolumn (Capcell Pak MF Ph-1), where unretained proteins were eluted to waste. Tofisopam was then eluted into an enrichment column using 13% acetonitrile in 50 mM phosphate buffer (pH 7.0) containing 5 mM sodium octanesulfonate and subsequently into the analytical column using 43% acetonitrile in 0.1% phosphoric acid containing 5 mM sodium octanesulfonate. The detection limit (2 ng/mL), good precision (CV < or = 4.2%) and speed (total analysis time 24 min) of the present method were sufficient for drug monitoring. This method was successfully applied to a bioequivalence test of two commercial tofisopam tablets.     

New heterometallic coordination polymers self-assembled from copper(II) nitrate and (diamine)Pt(II)(pyridinecarboxylates)(2)

One-dimensional (1-D), two-dimensional (2-D), and three-dimensional (3-D) coordination polymers were prepared by self-assembly of binary metal complex systems, copper(II) nitrate and (en)Pt(II)(nic)(2) or (dmpda)Pt(II)(isonic)(2) (en = ethylenediamine, dmpda = 2,2'-dimethyl-1,3-propanediamine, nic = nicotinate, and isonic = isonicotinate), in aqueous solutions. Equimolar reactions of copper(II) nitrate with (dmpda)Pt(II)(isonic)(2) and (en)Pt(II)(nic)(2) resulted in 1-D ([(dmpda)Pt(isonic)(2)Cu(OH(2))(3)](NO(3))(2))(n)() (1) and 2-D ([(en)Pt(nic)(2)Cu(OH(2))](NO(3))(2))(n) (2), respectively, but the reaction of (en)Pt(II)(nic)(2) with excess copper(II) nitrate gave 3-D ([((en)Pt(nic)(2))(3)Cu(5)(OH)(2)(OH(2))(6)](NO(3))(8))(n) (3). The local structure of crystal 1 has a mononuclear copper unit, 2 has a dinuclear copper unit with a Cu-Cu distance of 2.659(5) A, and 3 has a pentanuclear copper unit. The methyl groups of the dmpda ligand are located in the space between two isonicotinate ligands of 1, which is presumed to be an important factor to determine the final structure of the crystal formed by self-assembly. Magnetic behaviors of crystals 1-3 examined in the temperature range of 4-300 K appear to be governed by the local structures around the copper(II) ions and do not indicate any significant long-range magnetic exchange interactions along the polymeric chain.     

The site-selectivity and mechanism of Pd-catalyzed C(sp2)–H arylation of simple arenes

Control over site-selectivity is a critical challenge for practical application of catalytic C–H functionalization reactions in organic synthesis. Despite the seminal breakthrough of the Pd-catalyzed C(sp²)–H arylation of simple arenes via a concerted metalation–deprotonation (CMD) pathway in 2006, understanding the site-selectivity of the reaction still remains elusive. Here, we have comprehensively investigated the scope, site-selectivity, and mechanism of the Pd-catalyzed direct C–H arylation reaction of simple arenes. Counterintuitively, electron-rich arenes preferably undergo meta-arylation without the need for a specifically designed directing group, whereas electron-deficient arenes bearing fluoro or cyano groups exhibit high ortho-selectivity and electron-deficient arenes bearing bulky electron-withdrawing groups favor the meta-product. Comprehensive mechanistic investigations through a combination of kinetic measurements and stoichiometric experiments using arylpalladium complexes have revealed that the Pd-based catalytic system works via a cooperative bimetallic mechanism, not the originally proposed monometallic CMD mechanism, regardless of the presence of a strongly coordinating L-type ligand. Notably, the transmetalation step, which is influenced by a potassium cation, is suggested as the selectivity-determining step.

The transmetalation step, not the C–H activation step, is suggested as the selectivity-determining step in Pd-catalyzed C–H arylation of simple arenes.     

Two-dimensional packing patterns of amino acid surfactant and higher alcohols in an aqueous phase and their associated packing parameters

An amino acid surfactant, monosodium N-stearoyl-L-glutamate (MSSG), was assumed to associate with higher alcohols (HAs) in 1:1 molar ratio in an aqueous phase, and the packing parameters of the 1/1 MSSG/HA associates, Pa, were calculated by molecular dynamics (MD). Pa is defined as At1(l(t1)+l(t2))/a(h)l(t1), where At1 stands for the cross-sectional area of the MSSG tail, l(t1) for the length of the MSSG tail, l(t2) for the length of the HA tail, and a(h) for the area of the MSSG head group. The Pa value increased from 0.83 to 1.02 as the HA tail length (l(t2)) increased from C14 to C22. Associates of HAs having longer tails with MSSG are likely to fit better into bilayers because Pa is closer to 1 when l(t2) is longer. In the graphical results of the MD simulation for the association, however, a steric hindrance was found between the head groups of MSSG/HA when l(t2) was > or = C19. Based on this result, HA was classified into short-chain HA (SCHA, l(t2) < C19) and long-chain HA (LCHA, l(t2) > or = C19), and several possible packing units, composed of compositional combinations of MSSG, SCHA, and LCHA, were proposed. The packing unit is a building block which could constitute bilayers, and it is composed of variable compositional combinations of MSSG/HA. Assuming that SCHA associates with MSSG, the packing parameter, Punit, was calculated in a water box by MD for each packing unit. Punit is the packing parameter of a packing unit and it is defined as Vu/l(u)a(u), where Vu is the tail volume of the packing unit, l(u) is the chain length, and a(u) is the head area. For the calculation, stearyl alcohol (C18-OH, SA) was chosen as a SCHA and behenyl alcohol (C22-OH, BA) as a LCHA. When the compositional ratio MSSG:SCHA:LCHA was 1:1:1, Punit was around 1. The packing unit having Punit of around 1 formed a colloidally stable suspension for 30 days and its aggregate was a lamellar structure. However, the other packing units, for which Punit deviates significantly from 1, precipitated out in their suspensions and showed no evidence of a lamellar structure. According to the graphical MD simulations for the compositional MSSG/SCHA/LCHA associations in bilayers, vertical steric hindrance was found between LCHAs when Punit deviated significantly from 1. The steric hindrance would prevent the packing units from forming a stable bilayer and induce precipitation in the suspensions. Therefore, a proper combinational ratio of MSSG:LCHA:SCHA would play a major role in forming a lamellar structure.     

Melt polymerization of hexachlorocyclotriphosphazene in the presence of organotin (IV) compounds

The melt polymerization of hexachlorocyclotriphosphazene to poly(dichlorophosphazene) has been studied in the presence of organotin (IV) compounds. Unlike other typical Lewis acids, diethyltin (IV) chloride, Et₂SnCl₂, has shown to be an inhibitor for the thermal polymerization of the trimer, raising the activation energy to 70 kcal/mol. Diethyltin(IV) chloride remarkably delayed the rate of polymerization and efficiently inhibited the crosslinking reaction, thus leading to an improvement in the yield of the linear polymer without sacrifice to its molecular weight. © 1993 John Wiley & Sons, Inc.